This invention relates to a filamentary yarn useful for the weft component of a tire cord fabric and also to a tire cord fabric including such a yarn. More specifically this invention relates to a filamentary yarn being extendable uniformly and continuously during a tire building, especially during expansion of a carcass which comprises said yarn as the weft component of a tire cord fabric.
Heretofore, cotton yarns have been mainly used as the weft yarns in a tire cord fabric. But those skilled in the art have been keenly aware that cotton yarns raise various problems due to their excessive variation in strength and also their comparatively low extensibility. A typical example of these problems is the non-uniformity of a finished tire caused by uneven breakage of the weft yarns during expansion of a carcass by 60% to 80% to a toroidal shape during the building and vulcanizing to the tire.
To overcome these defects, Wolf et al. U.S. Pat. No. 3,395,744. suggests the adaptation, as the weft yarns in tire cord fabrics, of synthetic organic filaments in at least a partially unoriented state, having a high break elongation of at least 50%. Another proposal is made by Glass et al., U.S. Pat. No. 3,677,318, in which synthetic organic filaments having a high elongation of at least 80% are covered with cotton fibres, and these core spun yarns, when used as weft yarns, show an improved processing ability, especially in their even extensibility during the tire building process.
It seems that two proposals render satisfactory results as far as the prevention of breakage of the weft filaments is concerned. However, other important problems have been left unsolved. For example, filaments having a high break elongation of at least 50% which are in an undrawn state or in a transient state between the undrawn state and fully drawn state show an extremely unstable thermal property. Thus, a tire cord fabric comprising the above mentioned filaments has poor dimensional stability even at ambient temperature. Furthermore, when the fabric is subjected to a heat treatment, for example, the curing process of a resorcinol-formaldehyde-latex applied thereto at a temperature more than 240.degree. C., the weft filaments in the fabric become frail, losing their original extensibility.